The construction of underground water mains involves several steps. First trenches are dug to below the frost line for the underground water main, and each of the branches to each building. Next the water pipes are laid in the trenches and are connected together. Both ends of each underground water main are supplied with water, and underground water mains are placed periodically to allow any section to be isolated. At each branch there is also a shut off valve. This arrangement allows the branch, or either side of the main to be isolated.
Multi-part valve boxes are placed above the valve stem to create a channel to the surface, which is capped. When the cap is removed, and a valve wrench is lowered to the valve stem, the valve may be opened or shut from the surface. For the valve wrench to operate the valve, the valve box must be accurately located around the valve stem, and the valve box must be vertical or plumb.
The valve boxes are manually placed on the valve as the trench is being filled in and the dirt is being tamped. The valve box may be inaccurately placed laterally or may be moved, during the filling operation, by the machinery or by the uneven pressure of the untamped earth. The valve box may be inaccurately placed vertically, or bent at a joint, or may be moved during the filling operation. In either case, if the valve boxes are inaccurately placed, the valve wrench cannot turn the valve stem, and the valve box must be dug up and re-set.